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burnishing slipcast ware

updated sat 27 jan 01

 

Snail Scott on thu 25 jan 01


At 05:20 PM 1/25/01 +0000, you wrote:
>I have a friend who makes thrown and altered forms, then burnishes them,
>puts on terra sig, and saggar fires them. She's thinking about
>slip-casting some of these forms since it would be so much faster to
>make them. But someone told her that you can't burnish slipcast ware.
>Is this true? I have no idea since I've never burnished or slip-cast.
>Paul Lewing, Seattle


Low-fire casting slip takes a beautiful
burnish all by itself - no terra sig
needed! I have done this with work which
was low-bisqued and then rakued or smoke-
fired. Not quite as high a shine as terra
sig, but close. I burnish once at firm
leather-hard, then again when dry.

-Snail

Fredrick Paget on thu 25 jan 01


Yes - you can burnish slip-cast ware but you have to be extra careful to
support it while doing so and you have to catch it at the right point in
the drying cycle. The deflocculant makes it go all loosey-goosey when it is
rubbed and it gets flabby.
My experience is with slip-cast porcelain (a cone 10 body called Toshi
made by Laguna.)
I use a very smooth virgin teflon tool shaped like the back of a small
spoon and rub the surface while rotating it on the wheel. If you are doing
the outside of a bowl shape for instance, put it on a grabber pad or a
moistened wheelhead so it sticks in position and rotate it. Meanwhile
carefully burnish it with the teflon tool while holding it down on the pad
by using a flat disk or jar top to spread the force of the downward holding
pressure. You can do the inside while it is still in the mold.
Other shapes will require their own support methods.
The very low coefficient of friction of teflon - in other words it is very
slippery - make it a very good tool to use on the abrasive natured slip
casting clay.
Nobody that I know of makes and sells teflon tools anymore. They are too
labor intensive to make in small quantities. They could be molded in
expensive molds on expensive machinery but the market is too small for that.
They are not hard to cut out of virgin 1/4 inch thick white teflon sheet
stock (which sells for around $20 a square foot if you can find it).
They are shaped on a belt sander and finished off by wet sanding with
progressively finer grades of wet-or-dry carborundum auto body sand paper.
Start with 240 grit and go through 400, 600 and 1500 grits.
Fred Paget

>I have a friend who makes thrown and altered forms, then burnishes them,
>puts on terra sig, and saggar fires them. She's thinking about
>slip-casting some of these forms since it would be so much faster to
>make them. But someone told her that you can't burnish slip-cast ware.
>Is this true? I have no idea since I've never burnished or slip-cast.
>Paul Lewing, Seattle


>From Fred Paget, Marin County, California, USA

Paul Lewing on thu 25 jan 01


I have a friend who makes thrown and altered forms, then burnishes them,
puts on terra sig, and saggar fires them. She's thinking about
slip-casting some of these forms since it would be so much faster to
make them. But someone told her that you can't burnish slipcast ware.
Is this true? I have no idea since I've never burnished or slip-cast.
Paul Lewing, Seattle